JP2004039063A - Optical pickup and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To record data on a DVD-R and a DVD-RAM. <P>SOLUTION: An optical disk 10 is irradiated with a laser beam containing main and sub beams from an optical pickup 12, and a tracking error signal is generated by a differential push-pull method. When a DVD-R and a DVD-RAM are used as optical disks 10, a space in a track width direction between the main beam and the sub beam is set roughly equal to 1.85 μm. Thus, even for the DVD-RAM in which a distance between the land and the groove is 0.615 μm and the DVD-R in which the distance between the land and the groove is 0.37 μm, the main beam and the sub beam are radiated to enable differential push-pull. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical pickup and an optical disk device, and more particularly to a technique for recording and reproducing data on and from a plurality of types of optical disks.
[0002]
[Prior art]
The optical disc includes a CD-ROM, a CD-R, a CD-RW, a DVD-R, a DVD-RW, a DVD + RW, a DVD-RAM, and the like, which are used depending on the application. A read-only optical disk such as a CD-ROM has data formed of prepits, and reproduces data by a three-beam method. That is, one main beam and two sub beams are emitted from the optical pickup while being shifted by about 1/4 of the track pitch, and the reflected light is received. The reproduction signal is obtained from the sum signal of the main beam, and the tracking error signal is obtained by calculating the difference between the average levels of the sub beams.
[0003]
On the other hand, data recordable optical disks such as CD-Rs and DVD-RAMs have a land / groove structure, and record and reproduce data by a push-pull method. That is, the land / groove structure functions as a diffraction grating, and the laser light reflected on the disk surface produces light and dark on the light receiving element divided into two in the track width direction. A tracking error signal is obtained using the output difference. However, if the beam position on the light receiving element shifts due to the movement of the objective lens due to tracking or the like, an offset occurs in the output from the light receiving element, and the tracking error signal does not become zero even if the laser beam is at the center of the track. .
[0004]
Therefore, conventionally, a technology for removing an offset in the push-pull method has been developed. One method is to split a reflected laser beam into two by a hologram and to guide the reflected laser beam to each light receiving element, and the other method is to generate a main beam and a sub beam, and to take a differential between the main beam and the sub beam (differential push). Pull). In the differential push-pull, the main beam and the sub beam are shifted by の of the track pitch. For example, when recording in a groove, the main beam is radiated on the groove, and the sub beam is radiated on the adjacent land, so that the main beam is The difference between the push-pull signal and the push-pull signal of the sub beam is calculated. Since the main beam and the sub beam have the same amount of offset, the offset can be removed by calculating the differential.
[0005]
In the DVD-RAM, since data is recorded on both the land and the groove, the main beam and the sub beam are shifted by the track pitch, the main beam is irradiated on the groove, and the sub beam is irradiated on the adjacent land.
[0006]
[Problems to be solved by the invention]
As described above, when recording data on a DVD-R or DVD-RAM, a tracking error signal can be generated by irradiating a land and a groove with a main beam and a sub beam, respectively, and calculating a differential. Although it is possible, recently, there is a demand for recording and reproducing on and from various types of optical discs with one drive, and there has been a problem that conventional optical pickups or drives cannot cope.
[0007]
That is, when data is recorded on a DVD-R and a DVD-RAM, for example, the track pitches are different between the DVD-R and the DVD-RAM. Even if the optical system of the pickup is set, the main beam and the sub beam are not generally irradiated to the land and the groove in the DVD-RAM, and the tracking error signal cannot be generated even by using the differential push-pull. .
[0008]
Although it is theoretically possible to prepare optical systems for DVD-R and DVD-RAM and to switch between them, it is theoretically possible to cope with this, but this leads to an increase in the number of components of the optical pickup and an increase in cost.
[0009]
Japanese Patent Application Laid-Open No. 10-293939 discloses that when a tracking error signal is generated by a three-beam method, the main beam and the sub-beam are arranged so as to have a predetermined relationship so as to correspond to two types of optical recording media. Although the technique is described, it is not described when the differential push-pull method is used. Incidentally, when recording data on a DVD-R or DVD-RAM, the three-beam method cannot be used. During data recording, the sub beam preceding the main beam has a high reflected light level because no data has been recorded yet, while the sub beam following the main beam has a low reflected light level because the data has already been recorded, and Even if the difference between them is calculated, an effective tracking error signal cannot be obtained. The same is true even if the distance between the main beam and the sub beam is adjusted.
[0010]
The present invention has been made in view of the above-mentioned problems of the related art, and has as its object to provide an optical pickup capable of recording data on two types of optical disks having different track pitches, particularly, DVD-R and DVD-RAM. And an optical disk device.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an optical pickup for recording and reproducing data by irradiating an optical disc with laser light, comprising means for emitting laser light, and dividing the laser light into a main beam and a sub beam. Means for guiding the main beam and the sub-beam to the optical disk, and means for receiving reflected light of the main beam and the sub-beam from the optical disk and outputting a differential push-pull signal. The distance between the main beam and the sub beam in the track width direction on the optical disk is set to approximately 1.85 μm.
[0012]
The optical pickup of the present invention can be incorporated in an optical disk device that records and reproduces data on an optical disk. Such an optical disk device can record and reproduce data on either a DVD-R / DVD-RW / DVD + RW with a track pitch of 0.74 μm or a DVD-RAM with a track pitch of 0.615 μm.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 shows an overall configuration diagram of an optical disk device according to the present embodiment. An optical pickup (PU) 12 is arranged to face the optical disk 10, irradiates a laser beam onto the surface of the optical disk 10, and divides laser light emitted from the laser diode into one main beam and two sub beams. And an optical system for guiding the main beam and the sub-beam to the objective lens and an optical system for guiding the reflected light from the optical disk 10 to the photodetector. The laser diode is driven by a laser diode drive circuit (LDD) 32, and irradiates a laser beam of reproducing power when reproducing data, and irradiates a laser beam of recording power when recording.
[0015]
As the optical disk 10, a DVD-R (4.7 GB) and a DVD-RAM (4.7 GB) are used. That is, the optical disk device (drive) of the present embodiment records data on both the DVD-R and the DVD-RAM. The DVD-R has a land / groove structure, and records data only in the groove. The track pitch is 0.74 μm, which is the distance between adjacent grooves. On the other hand, a DVD-RAM also has a land / groove structure, and records data on lands and grooves. The track pitch is 0.615 μm as the distance between adjacent lands and grooves.
[0016]
Photodetectors of the optical pickup 12 are provided for the main beam and two sub-beams, respectively, similarly to the known configuration using the differential push-pull method, and detect signals corresponding to the amount of reflected light by the servo detector 14 and the RF. Output to the detection unit 20.
[0017]
The servo detection unit 14 generates a tracking error signal TE and a focus error signal FE based on the signal from the optical pickup 12 and outputs them to the tracking control unit 16 and the focus control unit 18, respectively. The tracking error signal TE is generated by a differential push-pull method, and the focus error signal FE is generated by an astigmatism method or the like. The tracking control unit 16 drives the optical pickup 12 in the track width direction of the optical disc 10 based on the tracking error signal TE to maintain the on-track state. The focus control unit 18 drives the optical pickup 12 in the focus direction based on the focus error signal FE to maintain the optical pickup 12 in the on-focus state.
[0018]
The RF detector 20 amplifies the signal from the optical pickup 12, specifically, the sum signal from the photodetector that receives the reflected light of the main beam, generates a reproduced RF signal, and outputs the reproduced RF signal to the signal processor 22 and the decoder 26. I do. The signal processing unit 22 detects a signal necessary for calculating a β value from a reproduced signal of test data at the time of performing OPC (Optical Power Control) and outputs the signal to the controller 30. The OPC means that when data is recorded on an optical disk capable of recording data, test data is recorded by changing the recording power to a predetermined area PCA in a plurality of steps, and the quality at the time of reproducing the test data is recorded. (Β value, jitter, etc.) to select the optimum recording power.
[0019]
The controller 30 calculates the β value, determines the optimum recording power for data recording, and controls the laser diode drive circuit 32.
[0020]
The decoder 26 includes an equalizer and a binarizer. The decoder 26 boosts a predetermined frequency of the reproduction RF signal, specifically, the amplitude of the 3T signal to binarize the signal, demodulates the binarized signal, and outputs the demodulated signal to the controller 30. Demodulation is performed by generating a synchronous clock signal with a PLL circuit (not shown) and extracting the signal. The controller 30 outputs the demodulated data from the decoder 26 to a host device such as a personal computer.
[0021]
FIG. 2 shows basic irradiation positions of a main beam and two sub beams in the differential push-pull method used in the present embodiment. When data is recorded in a groove, the main beam (main) is irradiated to the groove, and two sub beams (sub1 and sub2) are irradiated to lands adjacent to the groove. The push-pull is calculated for the main beam and the sub-beam, and the main and sub push-pulls are calculated. Since the offset occurs in the main beam and the sub beam by the same amount, the offset component is removed by calculating the differential. In addition, since the main beam and the sub-beam irradiate the groove and the land, the phases of the respective push-pull signals are inverted with each other, and when the differential between the main push-pull signal and the sub push-pull signal is calculated, the amplitude is doubled. When the optical disc 10 is a DVD-R, the main beam is applied to the inside of the groove, and the sub beam is applied to the land. When the optical disc 10 is a DVD-RAM, the main beam is applied to the inside of the groove or the land, and the sub beam is applied to the adjacent land or the groove.
[0022]
FIG. 3 shows a photodetector arrangement of the optical pickup 12 in the differential push-pull method. The four-divided photodetector 100 corresponds to the main beam, and the two photodetectors 102 and 104 divided into two in the track width direction correspond to the sub-beams 1 and 2, respectively. Assuming that the elements of the photodetectors 100, 102, and 104 are A to D, E1, E2, F1, and F2 as shown in the figure, the tracking error signal TE is, as described above, a differential between the main push-pull signal and the sub push-pull signal. TE = {(A + D) − (B + C)} − k {(E1 + F1) − (E2 + F2)}. k is a constant.
[0023]
By the way, since the distance between the land and the groove to be irradiated with the main beam and the sub-beam is different between the DVD-R and the DVD-RAM, the diffraction grating and the optical system of the optical pickup 12 should be adapted to the distance between one optical disk. If it is set, the land and the groove cannot be properly irradiated with the main beam and the sub beam on the other optical disk. Hereinafter, this point will be described.
[0024]
FIG. 4 shows a main beam and a sub beam (sub1) when the diffraction grating in the optical pickup 12 is set for DVD-RAM. FIG. 4A shows an irradiation position on the DVD-RAM, and FIG. 4B shows an irradiation position on the DVD-R. In a DVD-RAM, the distance between the land and the groove is 0.615 μm, and in the DVD-R, the distance between the land and the groove is 0.74 μm / 2 = 0.37 μm. Therefore, even if the main beam and the sub-beam are set to 0.615 μm in the DVD-RAM and the main beam is irradiated to the groove, and the sub-beam is irradiated to the adjacent land, the main beam and the sub-beam are each grooved in the DVD-R. And the land is not properly irradiated. (B) shows that the DVD-R irradiates the groove with the main beam, but irradiates the sub beam not on the center of the land but near the boundary between the land and the groove.
[0025]
On the other hand, FIG. 5 shows irradiation positions when the diffraction grating of the optical pickup 12 is set for DVD-R. In the figure, (a) shows the irradiation position on the DVD-R, and (b) shows the irradiation position on the DVD-RAM. Assuming that the interval between the main beam and the sub beam is 0.37 μm, the main beam and the sub beam are applied to the groove and the land in the DVD-R as shown in FIG. When recording is performed, the main beam and the sub beam are not correctly irradiated on the groove and the land. FIG. 2B shows that the sub-beam is irradiated not on the land but on the boundary between the groove and the land.
[0026]
When the distance between the main beam and the sub beam is set to 0.615 μm or 0.37 μm, data can be recorded only on one of the DVD-R and DVD-RAM, and the tracking error signal TE on the other. Cannot be generated and data cannot be recorded.
[0027]
Therefore, in the present embodiment, the distance between the main beam and the sub beam is set to a predetermined value, specifically, about 1.85 μm, so that the single optical pickup 12 can control the DVD-R and the DVD-RAM. Record the data.
[0028]
FIG. 6 shows irradiation positions of the main beam and the sub beam in the present embodiment. (A) is an irradiation position on a DVD-RAM, and (b) is an irradiation position on a DVD-R. Since the interval between the main beam and the sub-beam is set to approximately 1.85 μm, when the main beam is applied to the groove in the DVD-RAM, the sub-beam is applied to substantially the center of the land one distance away. On the other hand, in the DVD-R as well, by setting the interval between the main beam and the sub beam to be approximately 1.85 μm, the main beam is applied to the groove, and the sub beam is applied to the land two away from the land. As described above, in any case, the main beam and the sub-beam are irradiated on the groove and the land, so that the tracking error signal TE can be generated by the differential push-pull method using the main beam and the sub-beam.
[0029]
It is possible to irradiate the land and the groove in the DVD-RAM and DVD-R in the same manner even when the interval between the main beam and the sub beam is an integral multiple of 1.85 μm, but the distance between the main beam and the sub beam increases. As the size of the optical pickup 12 increases, it is desirable to set it near the minimum value of 1.85 μm.
[0030]
That is, there are a plurality of combinations of (m, n) such that 0.615 × m ≒ 0.37 × n (m, n = 1, 2, 3,...). It is desirable to choose one.
[0031]
Further, in the present embodiment, the distance between the main beam and the sub beam (the distance in the track width direction) is approximately 1.85 μm by adjusting the lattice constant of the diffraction grating in the optical pickup 12. May be located at the center of the groove, and the distance may be set to 0.615 × 3 = 1.845 μm so that the sub-beam is located at the center of the land one distance away. Further, in the DVD-R, the distance may be set to 0.370 × 5 = 1.850 μm so that the main beam is located at the center of the groove and the sub beam is located at the center of the land two distances away. In other words, when the main beam is located at the center of the groove, the sub beam is located not at the adjacent land but at the approximate center of one land apart from the adjacent land. It is to set so as to be located at substantially the center of a land, not two lands. Any numerical value can be set within the range of such a technical idea.
[0032]
In the present embodiment, the DVD-R is illustrated, but the present invention can be similarly applied to a case where a DVD-RW or a DVD + RW is used instead of the DVD-R.
[0033]
【The invention's effect】
As described above, according to the present invention, data can be recorded on different types of optical disks, particularly DVD-R / DVD-RW / DVD + RW and DVD-RAM, with a single optical pickup.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an embodiment.
FIG. 2 is an explanatory diagram showing irradiation positions of a main beam and a sub beam in a differential push-pull method.
FIG. 3 is a diagram illustrating the arrangement of photodetectors in a differential push-pull method.
FIG. 4 is an explanatory diagram of irradiation positions of a main beam and a sub beam in a DVD-R and a DVD-RAM (based on a DVD-RAM).
FIG. 5 is an explanatory diagram of the irradiation position of a main beam and a sub beam in a DVD-R and a DVD-RAM (based on a DVD-R).
FIG. 6 is an explanatory diagram of irradiation positions of a main beam and a sub beam on a DVD-R and a DVD-RAM according to the embodiment.
[Explanation of symbols]
Reference Signs List 10 optical disk, 12 optical pickup, 14 servo detector, 16 tracking controller, 18 focus controller, 20 RF detector, 22 signal processor, 26 decoder, 30 controller, 32 laser diode drive circuit.

Claims (3)

An optical pickup for recording and reproducing data by irradiating an optical disc with laser light,
Means for emitting laser light;
Splitting means for splitting the laser light into a main beam and a sub beam,
Means for guiding the main beam and the sub beam to the optical disc;
Means for receiving the reflected light of the main beam and the reflected light of the sub beam from the optical disc and outputting a differential push-pull signal,
An optical pickup, wherein a distance between the main beam and the sub beam in the track width direction on the optical disk is set to approximately 1.85 μm. An optical disk device comprising the optical pickup according to claim 1. The optical disk device according to claim 2,
An optical disc device for recording and reproducing data to or from a DVD-R / DVD-RW / DVD + RW having a track pitch of 0.74 μm or a DVD-RAM having a track pitch of 0.615 μm.

Images